Fix encoding error with Ruby 2.0

Fix the following error that occurs when running `socketio-client` with Ruby 2.0 or higher.

```bash
/Users/yasulab/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/socketio-client-0.0.3/lib/web_socket.rb:336:in `gets': encoding mismatch: ASCII-8BIT IO with UTF-8 RS (ArgumentError)
	from /Users/yasulab/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/socketio-client-0.0.3/lib/web_socket.rb:336:in `gets'
	from /Users/yasulab/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/socketio-client-0.0.3/lib/web_socket.rb:184:in `receive'
	from /Users/yasulab/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/socketio-client-0.0.3/lib/SocketIO.rb:67:in `block in start_recieve_loop'
```